Method of mixing and placing concrete

ABSTRACT

Concrete is produced by mixing cement with substantially the exact amount of water needed to produce a setting of the cement, and the mixture is then thoroughly agitated until its viscosity is substantially reduced. Dry sand or other aggregate is then added, and mixed with the slurry. This mixture is then pumped under pressure to a nozzle, which has an outlet passage tapering inwardly and ending in a transverse slot. Air under pressure is emitted in the form of jets into the tapering end part of the nozzle on the outside of the concrete mix flowing therethrough.

United States Patent Cornwell METHOD OF MIXING AND PLACING CONCRETE [72]Inventor: Charles E. Cornwell, Alexandria, Va. [73] Assignee: JenningsBailey, Jr., Frederick, Md. [22] Filed: Dec. 21, 1970 [21] Appl. No.:100,198

[52] U.S. Cl ..259/l47 [51] Int. Cl. ..B28c 5/06 [58] Field ofSearch..259/145, 146, 147, 148, 149, 259/151, 153, 154,4, 18

[56] References Cited UNITED STATES PATENTS 998,762 7/1911 Fallen.....259/l5l 2,316,705 4/1943 Morgan ..259/146 MIX 1? g I 6 HOPPER [15]3,669,417 [451 June 13, 1972 2,394,561 2/1946 Parkhurst ..259/1 512,758,945 8/1956 Widmayer .....259/l47 3,026,094 3/1962 True ..259/ l 47Primary Examiner-Robert W. Jenkins Attorney-Jennings Bailey, Jr.

[5 7] ABSTRACT 2 Claims, 5 Drawing Figures 17/1? MWESSOR PATENTEDJUNHI972 3.669.417

cavmsssoe W/VAEI? MIX 1? METHOD OF MIXING AND PLACING CONCRETEBACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to a method of placing concrete and to apparatus for usetherein.

2. The Prior Art It has been known in the past to spray a slurry ofconcrete containing water, cement and sand or aggregate. Such procedureshave not been particularly satisfactory because of the difficultiesinvolved in obtaining proper uniform consistency capable of beingprojected through a spray nozzle. Most cements when admixed with waterat the rate of 35-37 lbs. of water per 100 lbs. of cement produce asubstantially unworkable mixture, incapable of being sprayed orotherwise worked to a desired final form. The addition of more water tomake the product workable results in a decrease in the final strengthafter the cement is set.

When water, cement and aggregate such as sand are admixed in quantitiesnecessary to produce a workable product, because of the absorption ofsome of the water by the sand, extra water is required in order toprovide the amount necessary for reaction with the cement duringsetting. This extra water results in reduced strength in the final setproduct.

It has been found that the use of a slurry of the type according to theinvention causes totally impermissible wear on ordinary pumps, becauseof the abrasive nature of the slurry.

SUMMARY OF THE INVENTION Applicant has found that it is possible toproduce a concrete which when set has substantially greater strengththan normal concrete, without the requirement of expensive additives, bymixing together cement and just enough water to set the cement, thisbeing in most cases an amount of the order of 35-37 lbs. of water per100 lbs. of cement, and then subjecting the part having another inwardlytapering passage therein, the

inlet of which is substantially greater in diameter than the outlet ofthe first tapering passage. This second tapering passage terminates in aslit ofsubstantially greater length than the outlet part of the secondpassage but-of equal or somewhat less width. Provision is made forblowing air under pressure into the second passage at its larger end,this air acting to encase to a certain extent of the concrete flowingthrough the passage and further acting to enhance the spreading actionof the nozzle to give a fan effect.

In the normal mixing of concrete, a substantial part of the water isabsorbed in or on the aggregate particles, which means that asubstantial excess of water over that needed to react with the cementmust be used. On the other hand, in applying the process of the presentinvention, the slurry which comes into contact with the sand is absorbedonto or in the sand particles, so that a much better adhesion betweenthe particles is obtained, resulting in greater strength in the product.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows diagrammatically a system for carrying out the invention;

FIG. 2 shows a suitable blender;

FIG. 3 is a longitudinal cross-section through the nozzle;

FIG. 4 is a cross-section on the line 4-4 of FIG. 3; and

FIG. 5 is a cross-section on the line 5-5 of FIG. 3.

FIG. 1 of the drawings shows a system which includes a blender 2, inwhich water and-cement are admixed, in the quantities substantiallythose necessary to produce setting of the concrete. This with mostcements would be a proportion of about 35-37 lbs. of water to 100 lbs.of cement. From the blender, the slurry produced in a manner to bedescribed below goes to a mixer 4 in which it is admixed withsubstantially dry sand 100-150 lbs. for each 100 lbs. of cement) andthen to a hopper 6 from which it is pumped by a pump 8 through a valve10 to the nozzle 12. Air is supplied to the nozzle from an aircompressor 14.

A suitable type of blender is shown in FIG. 2. This is simply a tankwith a motor 16 driving through a shaft 18. a propeller 20. Thispropeller when driven at a high speed will be effective to agitate themixture of cement and water, causing cavitation which will draw. airdown into the bottom portion of the tank and produce more thoroughstirring action.

The slurry first formed in the blender 2 is very difiicult to handle,because of its high viscosity, but, if it is sufficiently agitated andstirred by the blade 20, its viscosity will be substantially reduced. Infact, the viscosity is sufficiently reduced so that it can be pumpedthrough the spray gun and will penetrate a number of layers of wire orexpanded metal. The sand being added, only just before it is sprayedfrom the gun, does not need to be wet, and therefore does not requireadditional water which would reduce the strength of the set concrete andimpair its setting properties. On the other hand, the sprayed concreteaccording to the invention does not set appreciably faster than anormally sprayed concrete mix.

The nozzle 12 is shown in detail in FIGS. 3 to 5. It includes a mainbody portion 22 adapted to be threaded onto the outlet 24 of valve 10.This body portion is formed of polyurethane, which is very resistant toabrasion by the cementicious material which is pumped through it. Thebody also contains, extending from the end of the valve outlet 24,apassage 26 tapering downward inwards the other end of the nozzle andending in an opening 28. Opening 28 opens into another tapering passage30 in a tip portion 34 of the valve also formed of polyurethane, whichhas a threaded ring portion 36 engaging in an annular groove in thefront end of the body 22. This tapering passage 30 starts with adiameter substantially larger than that of the opening 28 and tapersdown to about the same size as the opening 28. Thispassage is formed bya conical shaper. It is intersected at its outlet 40 by a slot 42 formedby a circular narrow grinding member and having its inner face in theform of a portion of a cylinder. 1

In the front end of the body 22is an annular chamber44, which connectsthrough an opening 46 to valve 10. There are a number of smallerpassages 48 leading from the annular chamber 44 to the inner or rear endof the passage 38, outside of the opening 28.

With this arrangement, when the device is in operation air underpressure of about 40 psi is admitted through holes 48 into the outerportion of the passage 38, while at the same time the pump 8 is pumpingthe concrete mixture into the passage 26. The material issuing from thenozzle forms a fan of substantially uniform consistency, which can besprayed on a backing such as expanded metal or the like or on anydesired rough material and will form ahard and impervious construction,of substantially greater strength than that made by normal methods.

The fact that the air is introduced at the very edge of the expansionchamber causes the material entering the expansion chamber to break upfrom an extruded substance to smaller individual pieces that are thenpropelled or accelerated through an identical sized exit to the surfacebeing sprayed.

The expansion chamber and air pressure control the material volume andthe actual consistency of the material being sprayed. By adjusting theair volume, the material can be sprayed with great impact on the surfaceand a very hard compaction is achieved.

The expansion chamber is contoured to provide a unique air circulationin the chamber and along the tapered sides to the viscous material,beating said material vigorously until its viscosity is substantiallyreduced to form a slurry, admixing substantially dry aggregate materialwith said slurry, and pumping the resulting mixture through a nozzlewhile introducing air under pressure on the outside of the materialflowing through the nozzle. I

2. A process as claimed in claim 1, in which the proportion of water tocement is substantially 35-37 lbs. of water per lbs. of cement.

* a nnw

2. A process as claimed in claim 1, in which the proportion of water tocement is substantially 35-37 lbs. of water per 100 lbs. of cement.